Abrasive machining is a mechanical process of removal of excess material from the surface of a metal or a nonmetal through the use of abrasives as cutting tools which at the same time produces a surface finish. The abrasive machining process comprises the general classification of (a) the precision type as exemplified by the related processes of grinding, lapping, and honing; and (b) the non-precision type as exemplified by the related processes of polishing and buffing. In precision abrasive machining the abrasive agent moves and the workpiece is stationary, or the workpiece moves and the abrasive is stationary. Surface material is removed within close size limits and the desired finish is obtained, whereas in non-precision abrasive machining surface material is removed until the desired finish is obtained. In non-precision abrasive machining the workpiece is usually held in contact with the abrasive surface by hand or vice versa.
Abrasive are of two main types -- natural and manufactured. Examples of abrasive stones found in nature are emery, sandstone, corundum. Silicon carbide and aluminum oxide are examples of the two most used abrasives. Diamonds can be classified as both natural and artificial.
Many kinds of machines have been built to bring the coated abrasive in contact with the workpiece. They may be broadly classified into two groups -- the endless belt machines and the coated abrasive wheels. The five main types of belt machines are platen, contact wheel, formed wheel, centerless, and flexible belt. (Lindberg, R. A. Processes and Materials of Manufacture. Boston, Mass., Allyn and Bacon, 1964. p. 669-672.) The platen machine provides a support or platen for part of the belt surface. All these machine designs have a common disadvantage and that is that the operator can not view the surface that is being abrading as it is being abraded. To do this the operator must pull the workpiece away from the abrading belt.